1. Field of the Invention
The present invention pertains to an insert rotary cutter having at least one first cutter insert and a least one second cutter insert for cutting off burrs attached to a cutter body.
2. Prior Art
In processing the surface of a metal workpiece by means of a insert rotary cutter, such as an insert face milling cutter (hereinafter referred to as a face milling cutter) having a plurality of cutter inserts thereon, burrs often remain at the edge of the processed surface of the workpiece. It is thought that the cause of burrs remaining is that the force to bend a small portion of the workpiece adjacent to the edge exceeds the shearing force to cut off the portion, and is that the small portion of the workpiece being bent by the cutting edge of the cutter insert toward the feeding direction of the face milling cutter prior to being cut off thoroughly by the cutting edge. Therefore, to avoid leaving burrs at the edge of the workpiece, the use of cutter inserts is recommended having sharp cutting edges attached on the milling cutter body with a high positive rake angle so as to reduce the force to bend which acts on the workpiece and to enable to cut the burr off thoroughly.
In addition to the above, it is well-known that a honed edge is inferior to an edge without honing to avoid leaving burrs, even if the honed edge has increased strength and prolonged service life. Accordingly, it is not adequate to employ a cutter insert having an honed edge in the processing to avoid leaving burrs.
On the contrary, in an insert rotary cutter having the sharp cutting edge without honing attached thereon with a high positive rake angle, the cutting edge tends to chip easily as its strength deteriorates Therefore, the insert rotary cutter of the kind referred to above, is not available for processing ordinary metal workpieces.
One conventional rotary cutter designed to leave no burrs on the processed surface of a workpiece is shown in Published Unexamined Japanese Patent Application No. 54-137187. This conventional insert rotary cutter has an equal number of first cutting edges and second cutting edges attached to a forward end of a tool body alternately in the circumferential direction; the second cutting edges are disposed radially inwardly and axially forwardly of the tool body with respect to the first cutting edges, thereby any burrs remaining on the surface processed by the first cutting edges will be swept off by the second cutting edge.
In the rotary cutter described above, however, new burrs are formed by the second cutting edge. Therefore, the rotary cutter is not capable of preventing the leaving of burrs on the processed surface of the workpiece.